An integrated microfluidic device in polyester for electrophoretic analysis of amino acids

Microfluidic immunoassay for rapid detection of cotinine in saliva

A microfluidic immunoassay is successfully developed for rapid analysis of cotinine saliva samples, which is a metabolite of nicotine and is widely used as a biomarker to evaluate the smoking status and exposure to tobacco smoke. The core microfluidic chip is fabricated by polydimethylsiloxane (PDMS) with standard soft lithography. Each chip is capable of eight parallel analyses of cotinine samples. The analyses can be completed within 40 min with 12 μl sample consumption. The linear detection range is 1 ~ 250 ng/ml and the minimum detectable concentration is 1 ng/ml respectively. The correlation coefficient of the calibration curve established from standard samples is 0.9989. The immunoassay was also validated by real saliva samples, and the results showed good reproducibility and accuracy. All the results were confirmed with traditional ELISA measurements. The result from microfluidic chip device and ELISA kits showed good correspondence, and the correlation coefficients are higher than 0.99. Compared with traditional technique, this microfluidic immunoassay is more economic, rapid, simple and sensitive, perfect for on-site cotinine measurements as well as for the evaluation of the exposure to tobacco smoking. Moreover, this immunoassay has potential to be applied in the analysis of other biomarkers in human saliva samples.

An integrated enzyme-linked immunosorbent assay system with an organic light-emitting diode and a charge-coupled device for fluorescence detection

A fluorescence detection system for a microfluidic device using an organic light-emitting diode (OLED) as the excitation light source and a charge-coupled device (CCD) as the photo detector was developed. The OLED was fabricated on a glass plate by photolithography and a vacuum deposition technique. The OLED produced a green luminescence with a peak emission at 512 nm and a half bandwidth of 55 nm. The maximum external quantum efficiency of the OLED was 7.2%. The emission intensity of the OLED at 10 mA/cm(2) was 13 μW (1.7 mW/cm(2)). The fluorescence detection system consisted of the OLED device, two band-pass filters, a five microchannel poly(dimethylsiloxane) (PDMS) microfluidic device and a linear CCD. The fluorescence detection system was successfully used in a flow-based enzyme-linked immunosorbent assay on a PDMS microfluidic device for the rapid determination of immunoglobulin A (IgA), a marker for human stress. The detection limit (S/N=3) for IgA was 16.5 ng/mL, and the sensitivity was sufficient for evaluating stress. Compared with the conventional 96-well microtiter plate assay, the analysis time and the amounts of reagent and sample solutions could all be reduced.

Microfluidics in protein chromatography

The development of microfluidics and its utilization in a myriad of applications has grown exponentially over the past 15 years. One area that has benefited from the great strides in fabrication of microelectromechanical systems (MEMS) is separations chemistry. Most studies have focused on small molecule and DNA separations; few on protein chromatographic techniques on microchips. This review details recent developments in protein separations on microfluidic platforms and how MEMS have the potential for revolutionizing protein chromatography.

Micellar electrokinetic chromatography on microchips

This review highlights the methodological and instrumental developments in microchip micellar EKC (MCMEKC) from 1995. The combination of higher separation efficiencies in micellar EKC (MEKC) with high-speed separation in microchip electrophoresis (MCE) should provide high-throughput and high-performance analytical systems. The chip-based separation technique has received considerable attention due to its integration ability without any connector. This advantage allows the development of a multidimensional separation system. Several types of 2-D separation microchips are described in the review. Since complicated channel configurations can easily be fabricated on planar substrates, various sample manipulations can be carried out prior to MCMEKC separations. For example, mixing for on-chip reactions, on-line sample preconcentration, on-chip assay, etc., have been integrated on MEKC microchips. The application of on-line sample preconcentration to MCMEKC can provide not only sensitivity enhancement but also the elucidation of the preconcentration mechanism due to the visualization ability of MCE. The characteristics of these sample manipulations on MEKC microchips are presented in this review. The scope of applications in MCMEKC covers mainly biogenic compounds such as amino acids, peptides, proteins, biogenic amines, DNA, and oestrogens. This review provides a comprehensive table listing the applications in MCMEKC in relation to detection methods.

Development of an integrated direct-contacting optical-fiber microchip with light-emitting diode-induced fluorescence detection

In this paper, one poly(dimethylsiloxane) (PDMS) sandwich microchip integrated with one direct-contacting optical fiber was fabricated by using a thin-casting method. This novel integrated PDMS sandwich microchip included top glass plate, PDMS membrane replica with microfluidic networks and optical fiber, flat PDMS membrane and bottom glass plate. As the tip of excitation optical fiber completely contacted with the separation microchannel in this integrated microchip, it not only increased the excitation light intensity to achieve the high sensitivity, but also reduced the diameter of excitation beam to obtain high resolution. In addition, we found that this rigid PDMS sandwich microchip structure effectively prevented PDMS microchannel distortion from rigid optical fiber, and provided a substantial convenience for microchips manipulating. A blue light-emitting diode (LED) was applied as excitation source by using optical fiber to couple excitation light into its direct-contacting microchannel for fluorescence detection. The performances of this integrated PDMS sandwich microchip was demonstrated by separating the mixture of sodium fluorescein (SF) and fluorescein isothiocyanate isomer I (FITC), and showed a higher sensitive and resolution than those obtained from the conventional integrated optical-fiber PDMS microchip with a 100-microm distance between fiber tip and separation microchannel. Additionally, the reproducibility of this integrated microchip with LED-induced fluorescence detection was also examined by separation of a mixture of FITC-labeled amino acids.

Determination of neurotransmitters in PC 12 cells by microchip electrophoresis with fluorescence detection

A sensitive fluorescence detection system with an Hg-lamp as the excitation source and a photon counter as the detector for microchip CE (MCE) has been developed. O-Phthaldialdehyde (OPA, lambda(ex) = 340 nm) was employed to label the catecholamine neurotransmitters such as dopamine (DA), norepinephrine (NE), and amino acid neurotransmitters including alanine (Ala), taurine (Tau), glycine (Gly), glutamic acid (Glu), and aspartic acid (Asp). The separation of seven derivatized neurotransmitters was successfully performed in MCE and the detection limits (S/N = 3) for DA, NE, Ala, Tau, Gly, Glu, and Asp were 0.85, 0.49, 0.23, 0.15, 0.13, 0.18, and 0.29 fmol, respectively. The system was then successfully applied for separation and determination of neurotransmitters in rat pheochromocytoma (PC 12) cells, and the average amounts of analyte per cell from a cell population were 2.5 fmol for DA, 3.3 fmol for Ala, 8.2 fmol for Tau, 4.0 fmol for Gly, and 1.9 fmol for Glu, respectively. By single-cell injection mode, electrophoresis separation and quantitative measurement of Glu in individual PC 12 cells was obtained. The average value of Glu per cell from single PC 12 cells analysis was found to be 3.5 +/- 3.1 fmol.

Recent developments in optical detection methods for microchip separations

This paper summarizes the features and performances of optical detection systems currently applied in order to monitor separations on microchip devices. Fluorescence detection, which delivers very high sensitivity and selectivity, is still the most widely applied method of detection. Instruments utilizing laser-induced fluorescence (LIF) and lamp-based fluorescence along with recent applications of light-emitting diodes (LED) as excitation sources are also covered in this paper. Since chemiluminescence detection can be achieved using extremely simple devices which no longer require light sources and optical components for focusing and collimation, interesting approaches based on this technique are presented, too. Although UV/vis absorbance is a detection method that is commonly used in standard desktop electrophoresis and liquid chromatography instruments, it has not yet reached the same level of popularity for microchip applications. Current applications of UV/vis absorbance detection to microchip separations and innovative approaches that increase sensitivity are described. This article, which contains 85 references, focuses on developments and applications published within the last three years, points out exciting new approaches, and provides future perspectives on this field.

Capillary electrophoresis with a UV light-emitting diode source for chemical monitoring of native and derivatized fluorescent compounds

We report the utilization of a high power UV light-emitting diode for fluorescence detection (UV-LED-IF) in CE separations. CE-UV-LED-IF allows analysis of a range of environmentally and biologically important compounds, including PAHs and biogenic amines, including neurotransmitters, amino acids, proteins, and peptides, that have been derivatized with UV-excited fluorogenic labels, e.g., o-phthalic dicarboxaldehyde/beta-mercaptoethanol (OPA/beta-ME). The 365 nm UV-LED was used as a stable, low cost source for detection of UV-excited fluorescent compounds. UV-LED-IF was used with both zonal CE separations and MEKC. Native fluorescence detection of PAHs was accomplished with detection limits ranging from 10 nM to 1.3 microM. Detection limits for OPA/beta-ME-labeled glutamic acid and aspartic acid were 11 and 10 nM, respectively, for off-line labeling, and 47 and 47 nM, respectively, for on-line labeling, comparable to UV-laser-based systems. Analysis of OPA/beta-ME-labeled proteins and peptides was performed with 28 and 47 nM detection limits for BSA and myoglobin, respectively.

Highly efficient dynamic modification of plastic microfluidic devices using proteins in microchip capillary electrophoresis

New dynamic coating agents were investigated for the manipulation of electroosmotic flow (EOF) in poly(methylmethacrylate) (PMMA) microchips. Blocking proteins designed for enzyme-linked immunosorbent assay (ELISA) applications (e.g. Block Ace and UltraBlock), and egg-white lysozyme were proposed in this study. The EOF could be enhanced, suppressed or its direction could be reversed, depending on the buffer pH and the charge on the proteins. The coating procedure is simple, requiring only filling of the microchannels with a coating solution, followed by a rinse with a running buffer solution prior to analysis. One major advantage of this method is that it is not necessary to add the coating agent to the running buffer solution. Block Ace and UltraBlock coatings were stable for at least five runs in a given microchannel without the need to condition the coating between runs other than replenishing the buffer solution after each run, i.e. the RSD values of EOF (n=5) were less than 4.3%, and there was no significant change in the EOF after 5 runs. The reproducibility of the coating procedures was found from the channel-to-channel RSD values of the EOF, and were less than 5.0% when using HEPES-Na buffer (pH 7.4) as the running buffer. Several examples of electrophoretic separations of amino acids and biogenic amines derivatized with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) are demonstrated in this paper. The dynamic coating method has the potential for a broad range of applications in microchip capillary electrophoresis (microchip CE) separations.

Low-picomolar limits of detection using high-power light-emitting diodes for fluorescence

Fluorescence detectors are ever more frequently being used with light-emitting diodes (LEDs) as the light source. Technological advances in the solid-state lighting industry have produced LEDs which are also suitable tools in analytical measurements. LEDs are now available which deliver 700 mW of radiometric power. While this greater light power can increase the fluorescence signal, it is not trivial to make proper use of this light. This new generation of LEDs has a large emitting area and a highly divergent beam. This presents a classic problem in optics where one must choose between either a small focused light spot, or high light collection efficiency. We have selected for light collection efficiency, which yields a light spot somewhat larger than the emitting area of the LED. This light is focused onto a flow cell. Increasing the detector cell internal diameter (i.d.) produces gains in (sensitivity)3. However, since the detector cell i.d. is smaller than the LED spot size, scattering of excitation light towards the detector remains a significant source of background signal. This can be minimized through the use of spectral filters and spatial filters in the form of pinholes. The detector produced a limit of detection (LOD) of 3 pM, which is roughly three orders of magnitude lower than other reports of LED-based fluorescence detectors. Furthermore, this LOD comes within a factor of six of much more expensive laser-based fluorescence systems. This detector has been used to monitor a separation from a gel filtration column of fluorescently labeled BSA from residual labeling reagent. The LOD of fluorescently labeled BSA is 25 pM.